By far performed spinal surgery is a lumbar laminectomy, which is frequently combined with a discectomy, fusion, or both. A laminectomy entails the removal of a portion of bone from the lamina from the posterior aspect of the spine to gain entrance into the spinal canal which contains the neural elements, and to provide access to the disc.
It is therefore necessary to separate the flavum from the lamina prior to removal of the bone. However, this task is complicated by the fact that the inferior laminar surface is neither straight nor flat. Therefore, if an attempt is made to separate the flavum from the bone with a flat edged instrument, such an instrument will get into the substance of the ligament causing delamination within the ligament, and without achieving the desired separation of the ligament from the lamina. This problem is compounded by the fact that while the Ligamentum Flavum is very fibrous and strong, immediately beneath it is the extremely delicate and vulnerable dural sac and the nerve roots. Surgeons have, while attempting to separate the flavum from the lamina, inadvertently plunged through into the spinal canal, rupturing the dural sac and causing neural injury.
The laminar bone is usually removed by using an up biting rongeur. However, the Ligamentum Flavum (literally yellow ligament) is extremely thick and is a firmly attached sheet of fibrous tissue running from the underside of one lamina to the underside of the next. The flavum acts as a significant impediment to the placement of the foot portion of the rongeur beneath the laminar bone to be removed.
The problem with this approach is that the rongeur foot has not been configured for this purpose and so significant force is required making that maneuver dangerous. Since the tip of the rongeur disappears from view as it is pushed under the lamina, one cannot tell if the rongeur, when closed, will bite bone alone, bone plus flavum, or if the tip has gone beyond the attachment of the flavum thus grasping the bone plus dural sac and nerve roots.
Another way to separate the flavum, presently in use, is by dissectors. Dissectors are strips of metal with edges that may be sharp or dull and whose overall configurations can be relatively straight along the longitudinal axes or which may have anywhere from a slight to a more pronounced curve or even be acutely angled such as a dental tool. As per the previous discussion, as these instruments have not been specifically designed for this specific purpose, they tend to either dig into the substance of the Ligamentum Flavum or to risk perforating the dural sac beneath.
Another group of instruments that are used are currettes. These surgical instruments have a handle and a shaft and terminate in an tip resembling a small cup. These instruments are primarily intended to be used for scooping out material, e.g. disc, or bone and are therefore sharpened along the inner wall of a cup so as to facilitate the cup's being filled as it passes through the tissue. As currettes are designed to have cups and to be sharpened in such a manner so as to facilitate the filling of those cups, they are really not appropriate for removing the flavum as the flavum is most effectively and safely removed as a sheet rather than in small cupful bits. Some surgeons attempt to use various currettes as side cutting knives beneath the lamina. This is ineffective because they are not capable of being sharpened in such a way as to facilitate this maneuver, and more importantly, because they are designed to hold tissue the cups have considerable depth in relation to their other dimensions such that if a curette were large enough to correspond to the extent of the flaval attachment, then its overall thickness would potentially pose a threat to the underlying nerves and dural sac which would be compressed or crushed.
There is therefore a need for an instrument specifically designed for the task of removing this flavum from the lamina and the use of which would be in such a manner as to safeguard the sanctity of the underlying neural contents.